Composite coated heat reflectors and infrared lamp heaters equipped therewith



May 20, 1969 R. c. LANGLEY 3,445,662

COMPOSITE COATED HEAT REFLECTORS AND INFRARED LAMP HEATERS EQUIPPEDTHERE-WITH Filed Dec. 28, 1964 Sheet 01'2 INTERDIFFUSION ANTl-GLARELAYER BARRIER LAYER 1 I n I IS IO \d' 13 METALLIC SUBSTRATE V llPRECIOUS METAL, e.g. GOLD, LINING f PRECIOUS METAL, 12.9 GOLD, LININGMETALLIC SUBSTRATE INTERDIFFUSION BARRIER LAYER INVENTOR. ROBERT C.LANGLEY BY f ATTOPAZ'Y COMPOSITE COATED HEAT REFLECTORS AND INFRAREDLAMP HEATERS EQUIPPED THEREWITH y 20, 1969 R. c. LANGLEY 3,445,662

Filed Dec. 28, 1964 Sheet 2 or 2 I NVENTOR.

ROBERT c. LANGLEY BY Arm/(W5? United States Patent 3,445,662 COMPOSITECOATED HEAT REFLECTORS AND INFRARED LAMP HEATERS EQUIPPED THEREWITI-IRobert C. Langley, Millington, N.J., assignor to Engelhard Minerals &Chemicals Corporation, a corporation of Delaware Filed Dec. 28, 1964,Ser. No. 421,247 The portion of the term of the patent subsequent toApr. 6, 1982, has been disclaimed Int. Cl. G21h 3/02 US. Cl. 25088Claims ABSTRACT OF THE DISCLOSURE An infrared lamp heater is disclosedwherein an infrared source is mounted in front of a reflector comprisinga metallic substrate having an infrared-reflective coating of a preciousmetal on its surface, and a refractory oxide diffusion barrier layerfrom 200 A. to 2000 A. thick between the reflective surface and themetallic substrate to prevent diffusion of the reflective coating intothe substrate.

This invention relates to heat reflectors and more especially tocomposite coated heat reflectors characterized by freedom frominterdiffusion of an infrared reflective thin precious metal coating orlining thereof and the metal of the reflector substrate or wall, and toinfrared lamp heaters incorporating the composite coated heatreflectors.

Infrared lamp heaters have been utilized experimentally heretofore as areplacement for electrical resistance element heating units in domesticcooking ranges. The infrared lamp heaters have a concav-o-convexmetallic "base with a thin coating of a precious metal such as gold onthe concave surface for purpose of reflecting the heat to the locus orplace where it will be utilized. A high intensity infrared source ismounted within the lamp envelope in front of the heat-reflectingcoating, and a glass plate or sheet is secured in front of the infraredsource in spaced relation thereto as part of the lamp envelope. Whilesuch lamp heaters are satisfactory in many respects for use in domesticcooking ranges, they suffer from the premature loss of theheat-reflective gold surface or coating. Thus the precious metal of theheatreflecting surface interdiffuses with the metal of the substrate orbase in a short time at an elevated temperature, for instance of 500 C.and higher, to the extent of actual disappearance of the precious metal,and hence the heat reflective surface is lost.

In accordance with the present invention, infrared lamp heaters areprovided which overcome and eliminate the problem of loss of theprecious metal heat-reflective surface by interdiifusion of the preciousmetal and the metal of the reflector substrate. The infrared lamp heaterof this invention comprises a metallic substrate having a concave innersurface, a thin adherent infrared-reflective lining or layer of aprecious metal over the concave surface, a thin barrier layer of arefractory oxide intermediate the infrared-reflective lining and themetallic substrate inner surface, and an infrared source mounted infront of the infrared reflective lining.

The barrier layer serves to prevent interdiffusion of the precious metalof the lining and the metal of the substrate inner surface normallyoccurring at high temperature in the absence of the barrier layer, tothe extent of actual disappearance of the precious metal.

In one embodiment of the lamp heater of this invention, a high intensityinfrared source, i.e. a source radiating infrared wavelengthsprincipally in the range of 3,445,662 Patented May 20, 1969 about0.753.0 microns, is mounted in front of the reflective lining. In thisembodiment, which is for use for high heat application, for instance asa heating unit in 'a domestic cooking range, an infrared-transmissivethermally refractory face member, preferably a plate or sheet, forinstance of a heat-resistant glass, is employed to complete the envelopeof the lamp heater. However, in another embodiment of the lamp heaterherein wherein an appreciably lower intensity infrared source, forinstance a source radiating longer wavelengths in the infrared such aswavelengths from 5.0 to 15.0 microns, is employed, for instance a lampheater for drying ink on a thermally unstable material such as paper, itis preferred no such face member be used due to the material offabrication of the face member absorbing materially at these longerwavelengths.

The high intensity infrared lamp heater is especially well suited foruse as a heating unit in a cooking range for the reason it is avirtually instantaneous source of high heat, as contrasted with theelectrical resistance element heating units which require a relativelylonger time and typically a period of minutes, to reach peaktemperature.

The diffusion barrier is essentially a thin layer, preferably ofthickness between about 200 and 2000 angstrom units. Such thinness ofthis barrier layer enables a materially better bonding of the outerprecious metal lining to the reflector metallic substrate or base thanwhen a layer of thickness much in excess of 2000 A. is used, despiteinherent differences between the three layers in expansion andcontraction with changes in temperature.

Refractory oxides suitable for the interdifiusion barrier layer are, forexample, CcO A1 0 BeO, Cr O HfO MgO, MnO, ThO Y O SiO ZnO and ZrO Theserefractory oxides are characterized by exhibiting good resistance tothermal shock and to material diffusion thereof into the metal base orsubstrate and into the precious metal of the liner and, in addition,have desirably high melting points. CeO has been found to be especiallywell suited for forming the interdiffusion barrier. The term refractoryoxide is used herein and in the appended claims in designating thematerial of the interdiffusion barrier layer in a broad sense, to meanan oxide of a metal, for instance a metal disclosed immediately above,or an oxide of a nonmetal, for instance silicon, and characterized byhaving good resistance to heat and heat shock, good stability to hightemperatures which may be encountered up to as high as 1200" C., andshowing good resistance to diffusion thereof into the precious metal ofthe liner and the metal of the base.

The precious metal of the infrared-reflective lining is preferably gold,due to its efficiency in reflecting wavelengths in the infrared regionand its resistance to oxidation. However, palladium, platinum or rhodiumor alloys of these metals can be utilized in place of the gold for theheat-reflective lining. The thin infrared-reflective lining ispreferably of thickness between about 200 and 2000 Angstrom units.

The material of the interditfusion barrier layer is applied over theinner metallic surface of the reflector wall or substrate as a thinlayer of a liquid composition comprising a thermally decomposable organocompound of the particular element, for instance an organo compound ofthe aluminum, cerium, silicon, beryllium, chromium, hafnium, magnesium,manganese, thorium, yttrium, zinc or zirconium, e.g. a soluble resinateof aluminum, cerium, silicon, beryllium or of one of the remainingelements, in solution in an organic solvent such as, for instance, theorganic solvents hereinafter disclosed for applying the precious metalinner lining by spraying or brushing, preferably spraying due to morereadily obtaining thinner and more uniform films. The applied solutionis then fired in air at a temperature of about 3000 C.-800 C. to driveoff the organic matter and deposit on the metallic surface a thin filmor coating of A1 or CeO One or a plurality of such coatings may beapplied as aforesaid depending upon the particular thickness desired,each coating when applied 'by spraying followed by firing as describedsupra having a typical thickness of about 200 A. described supra havinga typical thickness of about 200 A.

Examples of suitable compositions for applying the thin barrier layer bybrushing or spraying follow, parts and percentages being by weightunless otherwise specified.

Example I I Parts Cerium resinate dissolved in a mixture of oil ofrosemary, nitrobenzene and toluene (5% CeO 36.0 Rosin dissolved in oilof spike (50% rosin) 27.0 Oil of lavender 9.0 Oil of camphor 9.0 Oil ofpetitgrain 9.0

Example II Aluminum resinate dissolved in a mixture of oil of rosemary,nitrobenzene and toluene (5 A1 0 33.3 Rosin dissolved in oil of spike(50% rosin) 33.3

The soluble resinates of the metal of the interdifiusion barrier areprepared by reacting a soluble salt of the metal with rosin. Aluminumacetate can be reacted with rosin by heating a mixture of the twomaterials at temperature of about 150 C. The soluble resinate of siliconis prepared by heating at 120 C-l30 C. a mixture including silicontetrachloride and pine rosin as disclosed in US. Patent 2,842,457,column 7, lines 1l7. The solution resinate of cerium is prepared byreacting cerous hydroxide with the sodium salt of rosin at a temperatureof about 75 C. Exemplary of suitable solvents for preparing thesolutions for applicaiton are a mixture of essential oils; oil ofturpentine; and a mixture of oil of rosemary, nitrobenzene and toluene.

The infrared-reflective outer lining or coating is provided by applyingover the surface of the refractory oxide of the interdilfusion barrier,for instance by brushing or spraying, a thin coating of a liquidcomposition comprising a soluble thermally-decomposable organo compoundof the precious metal, for instance a soluble resinate of the gold,platinum, palladium or rhodium, and an organic solvent for the preciousmetal compound. Suitable solvents for preparing such compositions are amixture of essential oils; oil of turpentine; and a mixture of oil ofrosemary, nitrobenzene and chloroform. A flux for the precious metal isalso preferably present in such composition, for instance chromiumoxide, bismuth oxide, lead oxide and mixtures thereof. Application is byspraying or brushing. The article with applied solution is then fired in.air at a temperature within the range of about 150 C.900 C. todecompose the particular precious metal. One or a plurality of coatingsof the precious metal can be applied in the manner described dependingon the particular thickness desired. Each application yields a preciousmetal coating of typically about 1000 A. in thickness. A preferredtemperature for firing the gold Example IV Percent Gold resinatedissolved in a mixture of oil of rosemary, nitrobenzene .and ethylacetate (24% Au) 40 Rosin dissolved in oil of spike (3 0% rosin) 10 Oilof rosemary 30 chloroform 20 Example V Palladium resinate dissolved in amixture of oil of rosemary, nitrobenzene and chloroform (9% Pd) 50 Rosindissolved in oil of spike (30% rosin) 11 Oil of lavender 13 Oil ofcamphor 13 Oil of petitgrain 13 Example VI Platinum resinate dissolvedin a mixture of oil of rosemary, nitrobenzene and toluene (12% Pt) 50Rosin dissolved in terpineol (40% rosin) 10 Oil of lavender 20 Terpineol20 Example VII Rhodium resinate dissolved in a mixture of nitrobenzene,chloroform and oil of spike (5% Rh) 50 Rosin dissolved in oil of spike(30% rosin) 15 Chloroform 30 Terpineol 5 Example VIII Gold tertiarydodecyl mercaptide dissolved in a mixture of heptane and chloroform (28%Au) 20 Oil of peppermint 20 Terpineol 2 Toluene 29 Chloroform 29 Thehigh-intensity infrared lamp heater herein prefer ably has a thincontinuous, selective filter, anti-glare layer over the inner surface ofits infrared transmissive, thermally refractory face member, whichabsorbs the waves in the visible range but transmits the infrared waves.The selective filter layer enables the lamp heater to be utilizedwithout causing undue strain on a humans eyesight due to glare. Theselective filter, anti-glare layer is preferably of thickness in therange between about 500 A. and about 2000 A. Such layer is composed ofan intimate fused mixture of gold and a lesser amount of silver and aglass, the glass being obtained by the fusing together of SiO;, CaO andZnO as glass-making ingredients formed in situ during firing, andcooling of the fusion melt.

The selective filter, anti-glare layer is provided on the thermallyrefractory face member of the lamp, which face member is preferably of aheat-resistant glass, for instance a glass containing, by weight, 96%SiO and 4'% B 0 but which can be entirely of silica, by applying overthe surface of the refractory face or sheet intended to be the undersideor inner surface in the assembled lamp heater a thin coating of a liquidcomposition comprising a soluble thermally decomposable compound of goldand of silver, for instance gold resinate and silver resinate preparedby procedure similar to that previously disclosed herein for preparingthe metal resinates of the interdiffusion barrier layer, an organicsolvent for the organo compounds of gold and silver, and compatiblecompounds of silicon, calcium and zinc, for instance silicon resinate,calcium resinate and zinc resinate also prepared in accordance with themethod previously disclosed herein for preparation of the other metalresinates. Such composition is fired on the face member at a temperaturein the range of about 500 C.800 C. to decompose the organo compounds ofgold and silver and convert the organo compounds of silicon, calcium andzinc to their corresponding oxides, SiO CaO and ZnO, and the firing iscontinued at the higher end of the firing temperature range whereby theSiO CaO and ZnO fuse together. The fired layer is then cooled on therefractory face member to obtain thereon the thin selective filter,anti-glare layer mentioned supra. An especially suitable composition forapplication to the refractory face member for the lamp for forming theanti-glare layer is set forth in Example IX which follows.

Example IX Percent Gold resinate dissolved in a mixture of oil ofrosemary, nitrobenzene and ethyl acetate (24% Au) 17.5 Silver resinatedissolved in a mixture of oil of spike Oil of peppermint 10.0

The above solution after firing to obtain a film about 500 A. thick on asubstrate which transmits visible and short wavelength infrared energy,substantially reduces visible transmission while having little effect oninfrared transmission. The following table gives percent transmission ofthe uncoated substrate compared with the same substrate after coating.

Visible transmission Infrared transmission Wavelength (microns) 0. 4 0.5 0. 6 0. 7 0. 8 0. 9 1. 2.0

Uncoated. 91 91 92 91 91 90 90 90 Coated 15 32 73 84 87 87 81 Referenceis now made to the accompanying drawings wherein:

FIGURE 1 is a diagrammatic elevational sectional view of an infraredlamp heater of this invention;

FIGURE 2 is a diagrammatic elevational sectional view of a parabolicheat reflector of the invention;

FIGURE 3 is an end view partially broken away looking in the directionof the infrared transmissive refractory face member of the lamp heaterof FIGURE 1; and

FIGURE 4 is a perspective view of the infrared lamp heater herein.

Referring to FIGURES 1, 3 and 4 of the drawings, high intensity infraredlamp heater 10 has metallic substrate or wall 11 of parabolic shape inlongitudinal section and a paraboloid in its entirey of a high meltingmetal, for instance stainless steel. As shown in FIGURE 1, continuous,non-porous, adherent interdiflusion barrier layer 12 of thickness ofabout 1000 A. of the refractory oxide, for instance cerium oxide, isover substrate 11. Continuous, adherent, non-porous or substantiallynonporous infrared reflective lining or layer 13 of a precious metal,for instance gold, is over the barrier layer 12. High intensity infraredsource 14, for instance a tungsten filament sealed in a quartz envelopecontaining iodine therein, emits when heated high intensity infraredwaves, the infrared waves being reflected by precious metal film 13upwardly through anti-glare layer 15 and glass face plate 16 hereaftermentioned to the particular locus desired. Infrared source 14 is mountedin spaced relationship to reflective lining 13 and face plate 16. Thefilament of infrared source 14 is heated to a temperature of typicallyabout 2500 C.3000 C. for obtaining the emission of the wavelengths inthe range of about 0.75-3.0 microns; and to a filament temperature ofabout 500 C. to obtain a peak at a wavelength of about 5.0 microns, to afilament temperature of about 250 C. to obtain a peak at a wavelength ofabout 10 microns, and to a filament temperature of about C. to obtain apeak at a wavelength of about 15 microns. Conductor lead wires 14a and14b extending through small diameter orifices or passageways 22 and 23respectively, connect infrared source 14 to a source of electricalcurrent. Face plate 16 of an infrared transmissive, high heat resistantsilica glass known as Vycor and containing, by weight, 96% SiO and 4% B0 is positioned normal to the principal axis of lamp heater 10 andsealed at its lateral edge portion to metallic substrate 11 with the aidof gasketing with a high temperature polymer such as, for instance,Teflon. Continuous adherent substantially non-porousinfrared-transmitting, visible wavelength-absorbing layer 15 covers theunderside of face plate 16 and functions to prevent glare and attendantundue eye strain to humans. Lamp heater has a diameter at its face plate16 of about 6 /2, and a depth along its principal axis of about 5".

With reference to FIGURE 2, a composite coated infrared reflector unit18 is shown. Reflector unit 18 has concavo-convex metallic substrate 19,and continuous, non-porous, adherent interdiffusion barrier layer 20 ofthickness of about 1000 A. of the refractory oxide, for instance ceriumoxide, over the concave inner surface of substrate 19. Continuousadherent non-porous or substantially non-porous infrared-reflectivelayer 21 of a precious metal, for instance gold, is over barrier layer20. Reflector unit 18, in addition to being highly suitable for use inthe high intensity, infrared lamp heater of this invention, can be alsoutilized as a heat reflector in applications where less intense heat isrequired, e.g., in drying printing ink on paper. In such applications, alower intensity heat source, i.e., a source radiating at longerwavelengths in the infrared such as from 5.0 to 15.0 microns is used.Precious metals are very eflicient reflectors of energy of these longerwavelengths. In .a lower intensity heater it is preferred no face platebe used, since all known face-plate materials absorb appreciably at thelonger infrared wavelengths.

What is claimed is:

1. An infrared lamp heater comprising a metallic substrate having aconcave inner surface, a thin adherent infrared-reflective lining of aprecious metal over the substrate concave inner surface, a barrier layerof a refractory oxide having a thickness between about 200 A. and 200A.intermediate the infrared-reflective lining and the metallic substrateinner surface, the barrier layer preventing interdiffusion of theprecious metal of the reflective lining and the metal of the substrate,and an infrared source mounted in front of the infrared-reflectivelining.

2. The lamp heater of claim 1 wherein the infraredreflective lining isof gold.

3. A high intensity infrared lamp heater comprising an envelopeincluding a metallic substrate having a concave inner surface, a thinadherent infrared-reflective lining of a precious metal over thesubstrate concave inner surface, a barrier layer of a refractory oxidehaving a thickness between about 200 A. and 2000 A. intermediate theinfrared-reflective lining .and the metallic substrate inner surface,the barrier layer preventing interdiifusion of the precious metal of thereflective lining and the metal of the substrate, and aninfrared-transmissive thermally refractory face member: and ahigh-intensity infrared source mounted within the envelope in front ofthe infrared reflective lining.

4. The lamp heater of claim 3 wherein the infraredreflective lining isof gold.

5. The lamp heater of claim 3 wherein the barrier layer is of ceriumoxide.

6. The lamp heater of claim 3 wherein the infraredtransmissive,refractory face member is of a heat-resistant glass.

7. The lamp heater of claim 6 wherein the infraredtransmissive facemember has a thin, continuous, selective filter, anti-glare layer overits inner surface, the anti-glare layer being infrared-transmissive andvisible wavelength absorptive.

8. A heat reflector comprising a metallic substrate having a concaveinner surface, a thin adherent infraredreflective lining of a preciousmetal over the concave surface of the substrate, and a barrier layer ofa refractory oxide having a thickness between about 200 A. and 2000 A.intermediate the precious metal lining and the metallic substrateconcave surface, the barrier layer 8 preventing interdiffusion of theprecious metal of the lining and the metal of the substrate.

9. The reflector of claim 8 wherein the infrared-reflective lining is ofgold.

10. The reflector of claim 8 wherein the barrier layer is of ceriumoxide.

References Cited UNITED STATES PATENTS 2,501,563 3/1950 Colbert et a1.117-71 10 3,176,678 4/1965 Langley 1l771 3,188,513 6/ 1965 Hansler117-33.3 X 3,284,225 11/1966 Smock et a1.

ALFRED L. LEAVITT, Primary Examiner.

15 c. K. WEIFFENBACH, Assistant Examiner.

US. Cl. X.R.

